1. Field of the Invention
The present invention relates generally to printed circuit boards (PCBs), and more specifically to an apparatus for achieving PCB planarity during placement of surface mount components.
2. Description of the Prior Art
A variety of conventional techniques are currently used to place surface mount components on printed circuit boards (PCBs). Key to the success of these methods is the ability to achieve and maintain PCB planarity. Unless PCB planarity is maintained, it becomes very difficult to control the contact force used during the placement of surface mount components on the PCB.
These planarity and contact force concerns are aggravated when surface mount components must be placed on PCBs having vias. For PCBs having vias, some conventional methods, such as the vacuum and clamp method, are not feasible at all; a vacuum may not be achieved in a board having holes through it. Additionally, it is common practice for small individual PCBs having vias to be grouped together in panel form because of the convenience which panels offer. Often a number of small, connected PCBs, which may vary in size from less than one inch, are grouped to form a panel which may be 9 inches.times.11 inches or more. After surface mount components are placed on the PCBs, is easy to perform reflow, attach, and inspection procedures before separating the individual PCBs. Although the panels are convenient to process, they lack sufficient mechanical rigidity and PCB planarity. Routing between the PCBs means that the panel as a whole is not rigid and it is therefore very difficult to ensure the requisite planarity of individual PCBs. And, because of the panel's lack of rigidity, it is usually held to a planar surface only at peripheral points, such as the four corners, and not at individual points of interest during placement of the surface mount components, thereby contributing further to a lack of planarity in individual PCBs.